1. Field of the Invention
This invention relates to a process for selectively converting certain mono alkyl benzenes to para dialkyl benzenes, such as para ethyltoluene or para diethylbenzene, utilizing a specified crystalline aluminosilicate zeolite catalyst.
2. Description of the Prior Art
Alkylation of aromatic hydrocarbons utilizing crystalline aluminosilicate catalysts has theretofore been described. U.S. Pat. No. 2,904,697 to Mattox refers to alkylation of aromatic hydrocarbons with an olefin in the presence of a crystalline metallic aluminosilicate having uniform pore openings of about 6 to 15 Angstrom units. U.S. Pat. No. 3,251,897 to Wise describes alkylation of aromatic hydrocarbons in the presence of X- or Y-type crystalline aluminosilicate zeolites, specifically such type zeolites wherein the cation is rare earth and/or hydrogen. U.S. Pat. No. 3,751,504 to Keown et al. and U.S. Pat. No. 3,751,506 to Burress describe vapor phase alkylation of aromatic hydrocarbons with olefins, e.g. benzene with ethylene, in the presence of a ZSM-5 type zeolite catalyst.
While the above-noted prior art is considered of interest in connection with the subject matter of the present invention, the selective ethylation process described herein utilizing a catalyst of a crystalline aluminosilicate zeolite, said zeolite having a silica/alumina ratio of at least about 12 and a constraint index of 1 to 12, which catalyst has undergone prior modification to alter the activity and sorption characteristics thereof to achieve unexpectedly high selective production of para ethyltoluene or para diethylbenzene has not, insofar as is known, been heretofore described.
Both ethyltoluene and diethylbenzene are valuable chemicals. They may be dehydrogenated to produce the corresponding vinyltoluene and divinylbenzene. It has heretofore been recognized that the presence of substantial quantities of the ortho isomers are highly undesirable in the charge undergoing dehydrogenation since they tend to lead to ring closure with formation of the corresponding indenes and indanes which adversely affect the properties of the resultant polymer. The indenes and indanes are difficult to separate from the desired vinyl aromatic products. It has accordingly heretofore been necessary to remove the ortho isomers from the ethyltoluene and diethylbenzene charge stocks by expensive distillation techniques prior to dehydrogenation thereof.
It is evident that the availability of the ethyltoluene or diethylbenzene in which the ortho isomer is initially absent or present only in trace amount would eliminate the necessity for expensive prior removal of this isomer. Such products have, however, not heretofore been available.